Using Hawke’s Bay’s rivers to unlock the mysteries of marine carbon storage

Source: Radio New Zealand

Major research to test whether lowering the ocean’s acidity could help to fight climate change will get underway in Hawke’s Bay on Tuesday.

Over the next three weeks, New Zealand and Canadian researchers will use a small fleet of boats and watercraft to sample and map the chemistry of coastal waters in the region, especially around river mouths.

The voyage is part of a five-year, $11 million Endeavour Fund project, led by Earth Sciences New Zealand (ESNZ), to research the potential of several marine carbon dioxide removal (mCDR) techniques.

The ocean is already a massive natural carbon sink, but mCDR aims to draw extra carbon dioxide out of the rapidly warming atmosphere and lock more of it away in the deep ocean.

It has therefore attracted growing interest over the last decade or so, but many of the techniques – which involve adding things to the ocean to stimulate carbon removal – are only at a theoretical or lab testing stage.

ESNZ marine biogeochemist Cliff Law said that was partly because of how difficult it was to prove that any of them worked.

“When things spread in the ocean, it’s very difficult to actually have instruments in place to monitor it, because obviously the ocean’s a big wide place and it disperses quite randomly.”

There are also concerns about what effects marine carbon dioxide removal might have on the marine environment, which have driven a growing body of international law to restrict how the techniques are researched and deployed.

RNZ reported earlier this year on the international start-up Gigablue, which has attracted scepticism from some marine science experts over plans to carry out its own type of mCDR in New Zealand waters.

Instead of deliberately deploying any mCDR techniques, the ESNZ research would instead study their naturally-occurring equivalents, Law said.

Hawke’s Bay was the proving ground for the first of three processes, called ocean alkalinity.

“Alkalinity has been going into the oceans for millions and millions of years through things like rivers and from sediments,” he said.

“It provides a natural mechanism by which it offsets the acidity of the water. So in other words, it raises the pH and it absorbs the carbon dioxide, and it converts that into a dissolved form, which is no longer carbon dioxide, so it can’t be exchanged with the atmosphere.”

Rather than deliberately adding alkalinity to the ocean, the team would test how much carbon dioxide was being taken up as a result of Hawke’s Bay’s many rivers disgorging alkaline sediments and groundwater into the ocean.

“The reason why we looked in this region first of all was that we knew that there were limestone catchments and they tend to release more alkalinity into the fresh water,” Law said.

Canadian scientists would use ESNZ’s launch, Kimiora, to set a moored buoy with sensors, and would also operate an unmanned surface craft around the plume of water entering the bay from the Esk River.

“It’ll be mapping the surface waters and making measurements of… the carbon dioxide and the pH in the water, and from that, we can calculate the alkalinity.”

Further offshore, the ESNZ research vessel Tangaroa would move around southern Hawke’s Bay, Law said.

“We will be mapping the alkalinity, the salinity and the other things that will be indicators of the river input in the surface water. But we’ll also be making measurements throughout the water column.”

The team also planned to use an autonomous ‘glider’ craft that would move independently around the bay, collecting further measurements, including from the seafloor.

That would help the researchers to measure the effects of increased alkalinity on the marine environment, he said.

“If alkalinity has increased, what effect does it have on things like the phytoplankton and the sediments [on the seafloor]?”

ESNZ had already developed a good model of how river water and the alkalinity it carried mixed with the ocean, he said.

“The information we’ll get on this voyage will allow us to use the observations… to actually develop our measurements and our models.”

Later stages of the research would study natural equivalents for ocean fertilisation – when nutrients are added to the ocean to stimulate the growth of carbon-absorbing phytoplankton – and how much extra carbon can be stored if wood is deposited on the seafloor.

Rather than deliberate ocean fertilisation, the team would study what happened during a natural algal bloom, Law said.

“We’ll have a voyage in coming years down there to measure one of these phytoplankton blooms and measure the amount of carbon that’s falling out below it – how much is actually sequestered away in the deep ocean and where it goes.”

To study the effect of wood deposits, the team would look at the forestry slash that ended up on the seafloor in Hawke’s Bay because of Cyclone Gabrielle.

“We can look at how much of the carbon is still there and how much has been lost and how it’s impacted the biological communities in the sediment around it.”

Unlike the other two techniques, ocean alkalinity was a chemical process, making it slightly easier to monitor and measure, Law said.

“The real trouble with a lot of the biological marine CDR techniques is tracking the carbon, what its fate actually is, how much of it is going to get down into the deep ocean and be sequestered away for a long time?”

There were “all sorts of problems” with that.

“It can be broken down by feeding by animals and by bacteria, and it can be converted not only back into carbon dioxide quite quickly, but it can also be converted into other forms of carbon, which makes it difficult to monitor and measure and follow.”

Alkalinity, on the other hand, was a more straightforward chemical conversion of carbon dioxide into forms like bicarbonate.

“We know that it’s fairly stable in those forms for long periods of time – longer than 1000 years.”

The full research project aimed to answer important questions about what might happen if marine carbon dioxide removal did go ahead in future, Law said.

“What do we need to know? What are the risks? What are the benefits of these things? How will they impact ecosystems and the ocean’s chemistry? How much carbon dioxide could be removed? How do we actually monitor and verify them?”

That would help to inform New Zealand’s ministries and government “about whether this is an appropriate thing for us to be doing or not”, he said.

“If we were to go down this line, what do we need to know? What regulations do we need in place before we can even consider deploying something in our waters?”

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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand